is RP for me?

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melko
Posts: 19
Joined: Fri Aug 08, 2014 7:13 pm

is RP for me?

Post by melko » Sat Aug 09, 2014 11:31 am

I have a project to work on and I stumbled upon red pitaya, that seems to fit my needs, let me quickly explain what I have to achieve:

after a start signal that determine the init of the acquisition, I have a non-periodic (but let say with an average frequency of 1MHz) signal on which I have to acquire an analog signal with the ADC and store the result together with a time signature on the SD (or send it through ethernet or whatever..). This will least for about one hour, when then a stop signal rises.

The task is conceptually simple and RP seems perfect for it, but you know the devil hides behind details.
What I was thinking is to program the FPGA to start measuring time when the start signal rises, and when there's a trigger event, store the adc counts and the time measurement together in a dual clock FIFO, then CPU side read that data and store it on the SD or send it through eth (I could save it on a file through netfs, or use a UDP socket).

What do you think about it, is this feasible?

Crt Valentincic
Posts: 67
Joined: Wed May 28, 2014 12:15 pm

Re: is RP for me?

Post by Crt Valentincic » Tue Aug 12, 2014 12:03 am

Red Pitaya sure is the right solution. You could modify current FPGA acquisition module in order to start/stop
continuous acquisition on external trigger. A simple c program could be than used to detect that acquisition
has started and begin reading acquired data out of the circular buffer, storing it to SD card.
Depending on your timing/synchronization requirements there are also other possibilities to do this same thing
even without modifying FPGA logic. Simple continuous acquisition example
was discussed here.

melko
Posts: 19
Joined: Fri Aug 08, 2014 7:13 pm

Re: is RP for me?

Post by melko » Tue Aug 12, 2014 10:18 am

Thanks for the reply, seems I'll have to start persuading the project chief on buying one :)

Another question:
has the FPGA access to a clock, and if so what is the frequency?
Looking in the overview sheets of the zynq 7010 seems it doesn't say if the programmable logic part has access to a clock. I saw there's one on the board for the ADC, maybe it can be used for the FPGA too?

Nils Roos
Posts: 1441
Joined: Sat Jun 07, 2014 12:49 pm
Location: Königswinter

Re: is RP for me?

Post by Nils Roos » Tue Aug 12, 2014 10:25 pm

The FPGA fabric has access to quite a few clocks:
- 4 clocks (50, 125, 200, 250MHz) generated by the processor's PLL
- the external ADC clock
- DAC and daisy chain clocks generated by one of the two FPGA PLLs
- up to 4 additional clocks that you can generate and distribute to your heart's content with the remaining FPGA PLL and global clock buffers
- don't know if I missed anything

melko
Posts: 19
Joined: Fri Aug 08, 2014 7:13 pm

Re: is RP for me?

Post by melko » Thu Aug 28, 2014 8:35 pm

That's great, I guess 200MHz is more than enough for my needs!

About the sd, can be used a filesystem different from fat32 (e.g. ext3/4 or ntfs)? Also can it boot if the sd has more than one partition?

Scrolling through the Z7010's datasheet I see there's a 256KB on-chip SRAM accessible from both PS and PL, I wonder if it's fully available, it could be good for an improvement of the oscilloscope buffers' capabilities.

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